A simplified configuration of a system in which multiple motors share a common DC power supply is illustrated in FIG. 1. As shown in this figure, each of the motors is connected to the DC power supply via a DC bus. FIG. 1 further shows that the DC bus includes a capacitive element, e.g., one or more capacitors connected across the DC output terminals of the power supply.
In such systems, deceleration of a motor causes energy stored in the motor and/or load to return to the DC bus power supply. This energy, which is referred to as “regenerative energy,” is typically collected at the bus capacitor(s). In turn, the regenerative energy causes the voltage in the capacitors to increase, potentially to destructive levels.
An existing method for handling excess energy at the DC bus is to add a “slave axis,” as illustrated in FIG. 2. In such a system, the slave axis is used for storing energy or performing useful work, as necessary, to maintain a balance of power at the DC bus. Thus, the slave axis performs additional work, either by contributing to the overall effort of the system or by storing energy, e.g., using a mechanical fly-wheel.
However, adding this slave axis to the system creates additional weight for the system. In many types of systems, any additional weight becomes problematic. For example, in the aerospace industry, it is important to keep system weight to a minimum.
Other existing methods for handling excess energy require the addition of electronic and/or mechanical components specifically for the task of energy dissipation. One example, which is commonly referred to as “dynamic braking,” uses an additional power resistor and switch to dissipate energy. Although such methods may solve the problem of destructive voltage levels at the DC bus caused by regenerative energy, they impose additional costs on the system in the form of added components, increased weight, and other thermal concerns.
Thus, it would be advantageous to control the regenerative energy in the DC bus without adding any non-critical system components, such as a slave axis or dynamic braking components.